The present invention relates to placing physiological and chemical sensors, stimulating electrodes, and/or implantable fluid delivery/receiving systems within living tissue relative to the vascular or neurological anatomy of an animal or human patient to perform a measurement, sensing or stimulation function. More particularly, the invention relates to a replaceable catheter system for such sensors, electrodes and fluid delivery/receiving systems.
Catheter systems are utilized for numerous measurement, sensing, and stimulation functions of body fluids and tissues, typically through an invasive procedure in which the catheter is inserted within a vascular member, e.g., a vein or artery, through which the investigated fluid flows or the catheter is implanted within the investigated tissue.
U.S. Pat. Nos. 4,484,987; 4,650,547; 4,781,798; 4,627,906; 4,671,288; 4,703,756; 4,890,620; 5,190,041; 5,165,407; and 5,001,054 describe various forms of glucose sensing electrodes and systems for detecting variations in and levels of glucose in blood. These patents are incorporated herein by reference.
U.S. Pat. No. 4,373,527 issued to Fischell describes an implantable programmable medication infusion system for injecting controlled quantities of a medication such as insulin to correct for fluctuations and stabilize the level of glucose within a human in response to control information stored within the implantable system.
US. Pat. No. 4,494,950 also issued to Fischell, describes a medication delivery system including a plurality of modules implantable within and/or wearable by a patient. In particular, an implanted glucose sensor generates and transmits information to one or more implanted modules or modules wearable by a patient. One of the implanted modules may comprise a medication infusion system responsive to the signals from the glucose sensor module for regulating the delivery of insulin to the patient. This patent also describes a system wherein a glucose sensor is connected to the end of a needle inserted through the skin of the patient and connected by an electrical lead to an external signal processing module for telemetering data to an implanted module including a medication release system for dispensing controlled amounts of medication into the patient in response to the signals from the sensor. Being attached to the tip end of the needle, the glucose sensor may be readily replaced as needed. U.S. Pat. No. 4,494,950 is incorporated herein by reference.
The related art, such as the Fischell '950 patent, describe systems in which readily replaceable sensors are located just under a patient's skin and on a needle tip or a similar removable device. Surgically implanted in vivo sensors and/or electrodes, on the other hand, still require surgical removal with the associated expense and risks of infection to the patient. Accordingly, there is a continuing need for a system that allows for the implanting of physiological sensors, and/or electrodes deep within the body of a human in areas where it is desired to sense a predetermined physiological activity, to receive a body fluid for analysis, or to stimulate tissue; and wherein the sensor, tube, and/or an electrode may be readily replaced without engaging in an extensive, expensive and risky surgical procedure. Also, for situations where the sensor, tube, or electrode may need to be replaced frequently, e.g. every six months, while the remainder of the system with which the sensor, tube or electrode is used may last for some time, e.g. several years, it is desirable that the system accommodate replacement of only the sensor, tube or electrode portion while leaving the balance of the support system intact.
Further, there is a similar need for replaceability in implantable fluid dispensing or receiving systems in the event the fluid delivery or receiving tubes become clogged and require replacement. In such situations, it is desirable to provide a system which allows for the non-surgical replacement of the fluid delivery or receiving tubes from the implantable fluid dispenser, such as a drug pump.
An additional concern relates to complications that may arise from the presence of a catheter system within a patient. While most catheters are constructed of a biocompatible material, protective mechanisms of the body generally operate on the invasive device to protect the body from the invasion of the foreign object. The most common protective mechanism of the body is encapsulation of the foreign object by a growth of isolating tissue. Obviously, the encapsulation of the end of a catheter from which the sensor or electrode protrudes will significantly reduce or cease the desired operation of the in vivo device. Further, and in particular with regard to a catheter placed within a blood vessel, blood clotting may occur at the end of the catheter where a sensor extends or is exposed, resulting in reduced effectiveness of the in vivo device, as well as blockage of the vessel by the clot. This is clearly an undesirable result.
Antithrombogenic chemical substances are known which reduce and slow the formation of thrombus, tissue growth, blood clotting and the encapsulation mechanism. For example, the substance known as "heparin" is a known anticoagulant which inhibits the action of the enzyme thrombin in the final stage of coagulation. The use of such substances with catheters and probes to reduce the undesirable effects of the body's protective mechanisms is well known in the art. For example, U.S. Pat. No. 4,954,129, issued to Giuliani, et al., teaches the use of these chemical substances for hydraulic flushing of thrombus or clotting material from within the lumen of an intravascular catheter having an open end from which a sensor probe extends. The Giuliani et al. patent further provides a defined process for flushing the bore of the catheter which utilizes a periodically increased velocity pulse of a flushant to remove incipient clot material formations. A specific structure is described and claimed in the Giuliani patent for centering a sensor probe within the lumen of the catheter and away from the catheter wall. Such structure provides fluid channels for the flow of the flushant through and from the end of the catheter around the probe sensor.
Another U.S. Pat. No. 4,934,369, issued to Maxwell, deals with the subject problems in a similar manner. While Maxwell teaches the technique of flowing Antithrombogenic fluid through and out of the end of the intravascular catheter around the sensors for measuring blood constituents, Maxwell also teaches the positioning of the sensors within the catheter lumen a select distance from the opening at the end of the catheter. Blood is permitted to enter the end of the catheter and/or through ports about the circumference of the catheter and mix with the Antithrombogenic fluid to forming an interface zone therebetween. The blood-fluid interface zone is washed back and forth over the sensors to expose the sensors to both blood and Antithrombogenic fluid by one of various described means for pulsing the flow of fluid within the catheter lumen.
While these references appear to disclose functional systems for applying an Antithrombogenic fluid to the environment of a sensor, both concern catheters which have an opening at their distal end which permit the sensor exposure to blood, either by the sensor extending through the opening to come into contact with blood, or by blood entering the end opening to contact the sensor immediately adjacent therewith. In both constructions the Antithrombogenic fluid flows through the lumen of the catheter and exits the end of the catheter, requiring some means to position the sensor centrally within the end opening in order for it to obtain uniform exposure and for uniform fluid infusion. However, many applications require sensors that are positioned other than centrally within the lumen of a catheter. Thus, it is apparent that improvements are needed in the techniques and methods for reducing the undesirable effects of the body's protective mechanisms on surgically implanted devices and catheters.